The most widely employed method for the preparation of branched polyethylenimine is based on polymerization of ethylenimine produced from ethanolamine by the Wenker process. Polymerization of ethylenimine is effected in the presense of acids (such as hydrochloric acid) in solution or in bulk (cf. U.S. Pat. No. 2,182,306 /1936/, Cl. 260-239; British Pat. No. 466,270 /1935/, Cl. C3R). The resulting product is branched polyethylenimine with a molecular mass not exceeding 10,000.
A disadvantage of this prior art method is the use, as the starting compound, of ethylenimine which is a highly-toxic, carcinogenous and mutagenous agent necessitating carrying out the process in automated expensive systems without access of the personnel to the apparatus. Furthermore, the polymerization process is accompanied by evolution of considerable heat, wherefore it is hazardous; for the same reason, it is difficult to store ethylenimine liable to auto-polymerization. In the preparation of the starting ethylenimine there are formed large quantities of liquid wastes containing residual amounts of ethylenimine which should be dispersed with by combustion, thus adding-up to power consumption for the process on the whole. Moreover, the polymer yield obtained in this prior art method is about 60% as calculated for the starting ethylenimine.
The above-mentioned disadvantages are inherent in other known methods for the preparation of branched polyethylenimine, since in each known method the starting product is a toxic, carcinogenous and mutagenous ethylenimine.
Thus, known in the art is a method for preparing branched polyethylenimine by block polymerization of ethylenimine in the presence of sulphuric acid at the temperature of 100.degree. C. or in an aqueous solution at the temperature of 50.degree. C. (cf. J.Org.Chem., 30, 1994 /1965/). Branched polyethylenimine with the molecular mass of 1,600 can be prepared by polymerization of ethylenimine in the presence of 3 mol.% of acetic acid at the temperature of 50.degree. C. in a solution of methanol (J.Chem.Soc., 1956, 2448). Branched polyethylenimine with a higher molecular mass (30,000 to 40,000) can be prepared by polymerization of ethylenimine initiated by means of bifunctional alkylation agents such as epichlorohydrin (British Pat. No. 1,020,811 /1966/, Cl. C3R; U.S. Pat. No. 3,280,213 /1966/, Cl. 260-874).